The present invention relates to method and apparatus for particle image analysis, and more particularly to method and apparatus suitable for picking up and analyzing still images of particles suspended in a fluid sample flowed through a flow cell.
In prior art particle image analysis, in order to classify and analyze corpuscles in blood or cells and particles in urine, a sample is prepared on a slide glass and it is observed through a microscope. For the urine, since a particle density in the urine is low, the sample is previously centrifugally concentrated by a centrifugal separator before it is observed.
As a method or apparatus for automating the observation and the inspection procedures, a sample of blood, for example, is applied onto a slide glass which is then mounted on a microscope, and a microscope stage is automatically scanned and stopped at a position where particles are present to pick up a still particle image, and the particles in the sample are classified and analyzed by using feature extraction and pattern recognition methods by image processing techniques.
However, in the above method, it takes a long time to prepare the sample and perform the procedures to find the particles while mechanically moving the microscope stage for moving the particles to an appropriate image read area. Accordingly, a long time is required for the analysis and the mechanical structure is complicated.
As a particle image analysis method or a particle image analysis apparatus which does not need the preparation of the applied sample, a flow cytometer method has been known in which sample particles suspended in fluid are flowed through a flow cell and they are optically analyzed. The flow cytometer method observes a strength of fluorescence or scattered light from each particle in the sample and has a processing ability of 1000 particles per second.
Additionally, an attempt to pick up still particle images of particles in a continuously flowing sample and classifying and analyzing the particles from the respective still particle images has been made. An example thereof is disclosed in JP-A-7-83817.
According to the technique disclosed in JP-A-7-83817, particles picked up in one image which is picked up by an image pick-up unit and particles detected by a particle detection unit are correlated one to one. Thus, particles corresponding to the detected particles of the particles present in the image when a flash lamp light source is lit are counted from the particle detection signal, and the count is correlated to the detected particles of the particles present in the image to discriminate the particles which are not regarded as the detected particles from the detected particles. As a result, a complicated circuit configuration is required.